Back-pressure relief-valve.



PATENTED JAN. 24, 1905.

' G. A. CUNNINGHAM. BAGK PRESSURE RELIEF VALVE.

APPLICATION rum) Jun 6, 1904.

WITNESSES y INVENTOR 'Cbiiiz JFZL /z @gnihyiamy N ATTORNEYS UNITED STATES,

Patented January 24, 1905.

PATENT OFFICE.

COLIN ALLEN CUNNINGHAM, OF BRAINERD, MINNESOTA.

BACK-PRESSURE RELIEF-VALVE.

SPECIFICATION forming part of Letters Patent No. 780,866, dated January 24, 1905.

" Application filed June 6,1904. Serial No. 211,289.

To all whom, it mmtyoonccrnfl Be it known that I, COLIN ALLEN CUNNING- HAM, a citizen of the United States, and a resident of Brainerd, in the county of Crow Wing and State of Minnesota, have invented a new and Improved Back-Pressure Relief-Valve, of

which the following is a full,'clear, and exact to completely relieve the piston in the steamcylinder of all pressure over and above steamvchest pressure, thus insuring a steady running of the engine and utilization of the motive agent to the fullest advantage and relieving the piston of all pressure when the engine is drifting. I

The invention consists of novel features and parts and combinations of thesame, as will be more fully described hereinafter and then pointed out in the claims.

A practical embodiment'of the invention is represented in the accompanying drawings, forming a part of this specification, in which similar characters of reference indicate corresponding parts in all the views.

Figure 1 is a sectional side elevation of the improvement as applied to one end of the engine-cylinder and steam-chest. Fig. 2 is a sectional plan view of the improvement on the line 2 2 of Fig. 1. Fig. 3 is a sectional side elevation of the improvement provided with a cushioning-valve in the outlet, and Fig. 4

is a sectional plan view of the same on the line 44:0f Fig. 3.

On each end of the cylinder A of the locomotive steam-engine is externally secured an elbow B, on which is screwed orotherwise fastened a casing C, preferably made in three parts C, G and C of which the upper part 0 is closed by a screw-cap O and the lower 7 part O is secured to the elbow B. The lower part C of the casing is provided with a valveseat O 'on which is adapted tobe seated the valve D of a piston-valve D, having its piston D fitted snugly in the upper part 0 of the casing O, as plainly shown in Fig. 1. On the under side of the piston-valve D presses a spring E to normally hold the piston-valve D or outlets O leading to the outer air.

in an uppermost position with the valve D off the seat 0 to establish communication between the middlepart O of the casing, which middle part is provided with one or more ports Thus when the engine is drifting at the time the locomotive, say, is running down a hill,- then the piston in the cylinder A is prevented from pumping and compressing air, as each end of the cylinder is open to the atmosphere by way of therelief-valve, as described. v

The cap (J of the casing O is connected by a pipe F with the interior of the steam-chest G, so that the steam-chest'pressure is on the .top of the piston-valve D, and consequently presses the piston-valve D downward, so as to holdthe valve D on its seat while the engine is running; but when the piston in the cylinder A nears its end stroke and creates a pressure above that in the steam-chest G then this preponderance of pressure acts on the under side of the valve D to lift the piston- .valve, so as to open the valve-seat O to allow the preponderance of pressure to pass to the atmosphere by way of the open valve-seat O and the outlets O As soon as the pressure in the cylinder is reduced to that of the livesteam pressure in the steam-chest G then the piston-valve is again forced downward and the valve D moves to its seat O and the spring E is compressed.

If desired, a cushioning-valve H may be employed, and in this case the valve-casing H of the cushioning-valve H is provided with a single outlet O, registering with the space between the valve D and the piston D of the piston-valve D. The valve-casing H is provided with a valve-seat H on which is seated an outwardly-opening valve H normally held to its seat by a spring H arranged in the valve-casing H, opening with its outer end to the atmosphere. It is understood that valve D is held off its seat by the action of the spring E, I provide the valve H with a central port H leading to the outer air, so that air can pass into the part C of the casing even when the valve H is closed.

It is understood that when the steam is shut off from the engine the spring E immediately pushes the piston-valve D upward to move the valve D ofl its seat and to hold it off its seat until steam is again admitted to the steam-chest. By the arrangement described the piston-valve D is prevented from flopping, and a direct connection is had from the cylinder to the atmosphere. By the use of the cushioning-valve H the piston is prevented from pumping much air into the cylinder, and by having the port H in the said valve a vacuum is avoided in the part C and the piston-valve D is hence prevented from being drawn to its seat. The tension of the spring E is such as to compensate for the increase in area of the piston D over the valve D, so that the-piston-valve is moved upward by the spring E and the valve D is moved off its seat 0 as soon as the pressure in the cylinder rises above that in the steam-chest Gr.

Having thus described my invention, I claim as new and desire to secure by Letters Patent- 1. Aback-pressure relief-valve, comprising a casing connected at one end with the interior of the steam-cylinder and at the other end With the steam-chest, the casing having a valveseat at the end connected with the steam-cylinder and an outlet intermediate of its ends, said outlet leading to the atmosphere, and a piston-valve in the said casing, the valve of the piston-valve being adapted to be seated on the valve-seat and the piston being of a larger area than the piston-valve, and means for holding the valve from its seat when the piston is relieved of steam-chest pressure, whereby the cylinder is placed in communication with the atmosphere when the engine is drifting.

2. A back-pressure relief-valve, comprising a casing connected at one end with the interior of the steam-cylinder and at the other end with the steam-chest, the casing having a val veseat for connection with the steam cylinder and an outlet leading to the atmosphere, a piston-valve in the said casing, the valve of the piston-valve being adapted to be seated on the valve-seat and the piston being of a larger area than the piston-valve, and the said outlet beingintermediate the piston and the valve when thelatteris seated and the pressure from the steam-chest is on the piston, and a spring pressing the piston-valve to move and hold the valve off its seat when the piston is relieved of steam-chest pressure.

3. Abaek-pressurerelief-valve, comprising a casing connected at one end with the interior of the steam-cylinder and at the other end with the steam-chest,the casing having a val veseat for connection with the steam-cyliinler and an outlet leading to the atmosphere, a piston-valve in the said casing, the valve of the piston-valve being adapted to be seated on the valve-seat and the piston being of a larger area than the piston-valve and the said outlet being intermediate the piston and the valve when the latter is seated and the pressure from the steam-chest is on the piston, a spring pressing the piston-valve to move the valve off its seat, and a cushioning-valve in the said outlet.

4:. A back-pressure relief-valve, comprising a casing connected at one end with the interior of the steam-cylinder and at the other end with the steam-chest, the casing having a valveseat for connection with the steam-cylimler and an outlet leading to the atmosphere, a piston-valve in the said casing, the valve of the piston-valve being adapted to be seated on the valve-seat and the piston being of a larger area than the piston-valve and the said outlet being intermediate the piston and the valve when the latter is seated and the pressure from the steam-chest is on the piston, a s1 )ring pressing the piston-valve to move the valve off its seat, and a cushioning-valve in the said outlet, having a central port open at all times.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

COLIN ALLEN CUNNINGHAM. itnesses:

R. G. VALLENTYNE, JNO. N. NEVERS. 

